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Dust devils spotted at Mars probe’s landing site

The Context Camera on NASA’s Mars Reconnaissance Orbiter captured this image of two dust devils (marked with arrows) on 20 April

(Image: NASA/JPL-Caltech/MSSS)

The dust devils appeared at the centre of an oval-shaped region where the Phoenix lander is due to touch down

(Image: NASA/JPL-Caltech/MSSS)

Two whirling dust devils towering nearly a kilometre high have been seen at the exact spot where the Phoenix Mars lander is due to touch down in a few weeks. The dust vortices should pose no threat to the landing, but could provide dramatic views from the probe when it alights on the flat, relatively barren landscape.

Phoenix is due to land in an oval-shaped region dubbed “Green Valley” in Mars’s northern polar region on 25 May. In preparation for the landing, other spacecraft already at Mars, including NASA’s Mars Reconnaissance Orbiter (MRO), have been monitoring the site.

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On 20 April, MRO spotted two dust devils at the centre of the landing ellipse, which measures 20 by 100 kilometres across. Based on the shadows the dust devils cast on the surface, researchers estimate that one stretched to about 920 metres in height, while the other reached 790 metres.

Dust devils are created when vortices of air – set in motion when warm air rises from the surface on an otherwise still day – pick up dust from the ground. The dust reaches such great heights because of the Red Planet’s relatively low gravity.

“It’s the low gravity and the fact that the surface gets warm and the energy is transferred into turbulence and uplift within the atmosphere,” says Phoenix team member Ray Arvidson of Washington University in St Louis, Missouri, US.

Rising temperatures

Despite their enormous height, the vortices are not powerful enough to endanger any spacecraft. In fact, dust devils have cleaned dust off of the Mars rovers Spirit and Opportunity, allowing more sunlight to reach their solar panels.

“If we’re lucky, the occasional dust storm will help clear the dust off the deck and the solar panels,” Arvidson told New Scientist.

Dust devils will probably appear more and more often around Phoenix’s landing site in the coming months. That’s because the northern hemisphere is approaching summer (it will officially begin on 25 June), and more vortices are expected to occur as temperatures rise.

The kilometre-high dust devils, which have been caught on camera previously by the Spirit rover, could provide a dramatic sight for Phoenix, which is expected to operate for about 90 days at a single spot in the flat, chilly Green Valley.

Icy soil

“The topography should be pretty flat looking off into the horizon . . . so the dust devils should be easy to spot,” Arvidson says. He says Phoenix team members will try to make a movie of any dust devils observed by the lander, just as was done by the Spirit rover.

Phoenix also carries instruments – such as a lidar, a laser that looks straight up – that should be able to determine the size of dust particles. That could help researchers understand how much solar radiation reaches the surface and how much simply heats up the atmosphere.

“It would be good to have some dust devils moving through the area – both for science and cleanliness,” Arvidson says.

Phoenix will dig down as much as 50 centimetres below the surface, collecting samples of soil and ice that it will examine to better understand the region’s past climate and check for complex molecules that could be associated with life.

Mars Rovers – Mars is full of surprises, learn more in our continually updated special report.